Some New Ideas on Tectonic Evolution of Eastern China and Adjacent Areas

The major tectonic units of eastern China and its adjacent areas include five Precambrian massifs and four Phanerozoic orogenic belts. The formet are characterized by relatively small size and great tectonic mobility except for the Siberian platform; the latter are composite systems made up of a series of small oceanic basins and microcontinents occurring as island chains except for the South China zone. The integration of the various massifs involved a complex process of collision and welding. The related orogenic belts are thought to be polycyclic collision-imbrication ones rather than simple subduction-type or collision-type ones. The Yanshanian movement is the most important geologic event since the Phanerozic in this region. It was due to the Yanshanian orogeny that the above belts eventually accomplished their long-continued and complicated polycyclic orogenic processes, and the continental blocks were finally welded as a unity, becoming a part of the giant unified Eurasian cration. In the Middle Cretaceous, eastern Asia entered a completely new stage of tectonic development——the disintegration stage of continent. The eastern margin of Asia is not an accreted margin, but a destructed or disintegrated one.